The present invention relates generally to incinerator systems for the abatement of process emissions and, more particularly, to a three-bed regenerative fume incinerator system including a simplified valving arrangement for the control of hot gas flow to and from the beds of a regenerative incinerator.
Process emissions often contain combustible contaminants that, if released to the atmosphere, have the potential of polluting the environment. More particularly, noxious fumes, waste gas or process emissions generally contain contaminants in the form of volatile organic combustibles (VOCs).
However, the amount of combustible material contained in these emissions is generally below the concentration required to ignite or propagate a flame at ambient temperature. Accordingly, incinerators are employed to treat the process emissions by increasing the temperature of such process emissions to a temperature above the ignition temperature of the contaminants therein so as to oxidize the contaminants.
For increased efficiency, a regenerative incinerator system may be employed. Regenerative preheating increases the overall efficiency of the incinerator by minimizing the amount of fuel required to raise the process emissions to ignition temperature.
More particularly, as disclosed in Houston U.S. Pat. No. 3,870,474, and now commonly employed, an advantageous regenerative incinerator system has three regenerative beds, connected to a common combustion chamber. Each regenerative bed is filled with a suitable packing material, such as a multiplicity of heat retaining ceramic saddles. By means of appropriate valving to achieve three different operation cycles which sequentially and continuously repeat at intervals, the system is operated such that each bed, at different times, is a feed bed, a purge bed, and an exhaust bed. At any given time, gas flow in a three-bed regenerative incinerator system is such that hot gas from the combustion chamber heats the exhaust bed, while the feed bed (which previously was the exhaust bed) preheats incoming process emissions directed into the combustion chamber, and the purge bed (which previously was the feed bed) is purged into the combustion chamber.
As disclosed in Houston U.S. Pat. No. 3,870,474, having three beds in a regenerative incinerator system allows one bed to be a purge bed to avoid the leakage of even small amounts of untreated gas into the atmosphere. There do exist two-bed regenerative incinerator systems wherein the two beds alternate between the feed bed and the exhaust bed function, with the disadvantage that untreated gas remaining in the feed bed is exhausted to the atmosphere when gas flow through the beds reverses and the feed bed becomes the exhaust bed. Three-bed incinerators avoid this disadvantage, as the feed bed becomes the purge bed during the next operation cycle, with gas flow in that particular bed continuing in the same direction, towards the combustion chamber.
It will be appreciated that a suitable valving arrangement is required to control the gas flow and thus effect the operation cycles whereby the functions of the three regenerative beds are changed. It will further be appreciated that demanding requirements are placed on flow control valves in a regenerative incinerator application. The valves must be relatively large to handle a high volume of hot gas flow, and further must operate over a typical incinerator temperature range of 50.degree. F. to 1,000.degree. F. (10.degree. C. to 538.degree. C.), with attendant thermal expansion and contraction considerations.
The above-referenced Houston U.S. Pat. No. 3,870,474 discloses a system employing three three-way valves and three two-way (open or closed) valves, for a total of six valves. A more common arrangement, such as is disclosed in Houston U.S. Pat. Nos. 5,000,422 and 5,217,041 employs a total of nine two-way valves. Current commercial practice is to employ the nine two-way valve configuration, organized as six large power-operated two-way valves for controlling feed gas into and treated gas out of the three beds, and three medium-size power-operated two-way valves for controlling purge gas flow. The six large power-operated two-way valves in particular are expensive, and represent a significant portion of the total cost of a regenerative fume incinerator system. Moreover, a relatively complex control system must be provided to operate the nine valves at proper times and in an appropriate sequence to change the operation cycles at intervals.
A number of approaches to reducing the cost of valving for three-bed regenerative incinerators have been proposed in the prior art, but without apparent success in commercial practice. Examples are disclosed in Kuechler U.S. Pat. No. 3,634,026, Katabuchi et al U.S. Pat. No. 4,126,419, Edgerton U.S. Pat. No. 4,280,416, Benedict U.S. Pat. No. 4,454,826, and Thomason U.S. Pat. No. 5,016,547.